CN117980426A

CN117980426A - Optical adhesive sheet

Info

Publication number: CN117980426A
Application number: CN202280064189.3A
Authority: CN
Inventors: 渡边显士
Original assignee: Nitto Denko Corp
Current assignee: Nitto Denko Corp
Priority date: 2021-09-24
Filing date: 2022-09-02
Publication date: 2024-05-03
Also published as: WO2023047917A1; TW202323472A; JP2023047042A

Abstract

The adhesive sheet (10) of the present invention is an optical adhesive sheet. The adhesive sheet (10) has a peel strength F1 of 5N/20mm or more in the following low-speed peel test: the adhesive sheet (10) was attached to a glass plate and thereafter the resultant was subjected to heat and pressure treatment at 50℃under 0.5MPa for 15 minutes, and then the adhesive sheet (10) was peeled from the glass plate under conditions of 25℃at a peeling angle of 180℃and a drawing speed of 30 mm/min. The adhesive sheet (10) has a tensile adhesive strength B1 of 0.9N/mm ² or more in the following low-speed tensile test: the first glass plate and the second glass plate are joined in the thickness direction by an adhesive sheet (10) and thereafter subjected to the above-mentioned heat-pressing treatment, and then the first glass plate and the second glass plate are drawn on the opposite sides to each other in the thickness direction under the conditions of 25 ℃ and a drawing speed of 5 mm/min.

Description

Optical adhesive sheet

Technical Field

The present invention relates to an optical adhesive sheet.

Background

The display panel has, for example, a laminated structure including a pixel panel, a polarizing plate, a touch panel, a protective film, and the like. In the manufacturing process of such a display panel, a transparent adhesive sheet (optical adhesive sheet) for optical use is used in order to join elements included in a laminated structure to each other.

On the other hand, a repeatedly bendable (foldable) display panel for a smart phone and a tablet computer terminal, for example, is being developed. In particular, the foldable display panel is capable of repeatedly deforming between a curved shape and a flat non-curved shape. In such a foldable display panel, each element in the laminated structure can be repeatedly manufactured by bending, and a thin optical adhesive sheet is used for bonding between such elements. For example, patent document 1 below describes an optical pressure-sensitive adhesive sheet for flexible display panels such as foldable display panels.

Prior art literature

Patent literature

Patent document 1: japanese patent laid-open publication No. 2018-111754

Disclosure of Invention

Problems to be solved by the invention

As a flexible display panel, a display panel capable of being rolled up (rollable) is being developed. The rollable display panel can be repeatedly deformed between a rolled shape after being rolled up in whole or in part and a flat shape after being pulled out in whole, for example. In such a rollable display panel, each element in the laminated structure is made to be capable of repeated deformation, and a thin optical adhesive sheet is used for bonding between such elements. When the rollable display panel is in a rolled shape, the optical adhesive sheet joined to the element of the rolled shape is continuously subjected to stress from the element. Such an optical pressure-sensitive adhesive sheet is required to be less likely to be peeled off from an element to be adhered when the display is in a rolled shape at a very high level.

The present invention provides an optical adhesive sheet suitable for rollable display applications.

Means for solving the problems

The invention [1] comprises an optical adhesive sheet, wherein the optical adhesive sheet has a peel strength F1 of 5N/20mm or more in a low-speed peel test of: attaching the optical adhesive sheet to a glass plate and thereafter subjecting the resultant to heat and pressure treatment at 50 ℃ for 0.5MPa and 15 minutes, and then peeling the optical adhesive sheet from the glass plate at 25 ℃ at a peeling angle of 180 ° and a pulling speed of 30 mm/minute, the optical adhesive sheet having a pulling adhesive strength B1 of 0.9N/mm ² or more in a low-speed pulling test of: the first glass plate and the second glass plate were joined in the thickness direction by the optical adhesive sheet and thereafter subjected to the aforementioned heat-pressing treatment, and then the first glass plate and the second glass plate were drawn on the opposite sides to each other in the thickness direction under the conditions of 25 ℃ and a drawing speed of 5 mm/min.

The invention [2] comprises the optical adhesive sheet of the above [1], wherein the peel strength F1 (N/20 mm) and the pull adhesive strength B1 (N/mm ²) satisfy F1.gtoreq.1/3 XB1+7.

The invention [3] comprises the optical adhesive sheet described in the above [1] or [2], wherein the optical adhesive sheet has a peel strength F2 of 4N/20mm or more in the following low-speed peel test: the optical adhesive sheet was bonded to a glass plate and thereafter the resultant was subjected to the aforementioned heat and pressure treatment, and then the optical adhesive sheet was peeled off from the glass plate under conditions of 50 ℃ at a peeling angle of 180 ° and a pulling speed of 30 mm/min, and the optical adhesive sheet had a pulling adhesive strength B2 of 0.9N/mm ² or more in the following low-speed pulling test: the first glass plate and the second glass plate were joined in the thickness direction by the optical adhesive sheet and thereafter the resultant was subjected to the aforementioned heat and pressure treatment, and then the first glass plate and the second glass plate were drawn on the opposite sides to each other in the thickness direction under the conditions of 50 ℃ and a drawing speed of 5 mm/min.

The invention [4] comprises the optical adhesive sheet of the above [3], wherein the peel strength F2 (N/20 mm) and the pull adhesive strength B2 (N/mm ²) satisfy F2.gtoreq.1/3 XB2+5.

The invention [5] comprises the optical adhesive sheet according to any one of [1] to [4], wherein the optical adhesive sheet has a peel strength F3 of 3N/20mm or more in a low-speed peel test of: the optical adhesive sheet was bonded to a glass plate and thereafter the resultant was subjected to the aforementioned heat and pressure treatment, and then the optical adhesive sheet was peeled off from the glass plate under conditions of 80 ℃ at a peeling angle of 180 ° and a pulling speed of 30 mm/min, and the optical adhesive sheet had a pulling adhesive strength B3 of 0.9N/mm ² or more in the following low-speed pulling test: the first glass plate and the second glass plate were joined in the thickness direction by the optical adhesive sheet and thereafter subjected to the aforementioned heat and pressure treatment, and then the first glass plate and the second glass plate were drawn on the opposite sides to each other in the thickness direction under conditions of 80 ℃ and a drawing speed of 5 mm/min.

The invention [6] comprises the optical adhesive sheet according to any one of [1] to [5], wherein the ratio of the peel strength F4 to the peel strength F1 in the low-speed peel test of: the optical adhesive sheet was bonded to a glass plate and thereafter the resultant was subjected to the aforementioned heat and pressure treatment, and then the optical adhesive sheet was peeled from the glass plate under conditions of 95℃and a peeling angle of 180℃and a drawing speed of 30 mm/min.

The invention [7] comprises the optical adhesive sheet according to any one of [1] to [6], wherein the ratio of the peel strength F5 to the peel strength F1 in the low-speed peel test of: the optical adhesive sheet was attached to a glass plate and thereafter the resultant was subjected to the aforementioned heat and pressure treatment, and then the optical adhesive sheet was peeled from the glass plate under conditions of 65℃and a relative humidity of 90%, a peeling angle of 180℃and a drawing speed of 30 mm/min.

Effects of the invention

The optical adhesive sheet of the present invention has a peel strength of 5N/20mm or more in the low-speed peel test at 25 ℃ and a pull adhesive strength of 0.9N/mm ² or more in the low-speed pull test at 25 ℃. Such an optical adhesive sheet having high adhesion strength as measured in a low-speed test is suitable for ensuring good adhesion to an adherend and suppressing peeling from the adherend when the adherend is continuously subjected to stress from the adherend in a state where the adherend to which the adhesive sheet is adhered is wound. Thus, the optical adhesive sheet is suitable for rollable display applications.

Drawings

Fig. 1 is a schematic cross-sectional view of an embodiment of the optical adhesive sheet of the present invention.

Fig. 2 shows an example of a method of using the optical pressure-sensitive adhesive sheet of the present invention. Fig. 2A shows a step of bonding an optical adhesive sheet to a first adherend, fig. 2B shows a step of bonding the first adherend and a second adherend by the optical adhesive sheet, and fig. 2C shows a curing step.

Fig. 3 is a graph obtained by plotting measurement results of tensile adhesive strength (horizontal axis) and peel strength (vertical axis) measured for the optical adhesive sheets of examples and comparative examples.

Detailed Description

As shown in fig. 1, an adhesive sheet 10, which is an embodiment of the optical adhesive sheet of the present invention, has a sheet shape of a predetermined thickness and extends in a direction (plane direction) orthogonal to the thickness direction. The pressure-sensitive adhesive sheet 10 has a pressure-sensitive adhesive surface 11 (first pressure-sensitive adhesive surface) on one surface in the thickness direction H and a pressure-sensitive adhesive surface 12 (second pressure-sensitive adhesive surface) on the other surface in the thickness direction H. Fig. 1 illustrates a state in which release liners L1, L2 are attached to the adhesive surfaces 11, 12 of the adhesive sheet 10. The release liner L1 is disposed on the adhesive surface 11. The release liner L2 is disposed on the adhesive surface 12.

Such an adhesive sheet 10 is a transparent adhesive sheet (optical adhesive sheet) to be disposed at a light passing portion in a rollable display panel. The rollable display panel has, for example, a laminated structure including a pixel panel, a polarizing plate (polarizing film), a touch panel, a protective film, and the like. Examples of the rollable display panel include: display panel, on-vehicle display panel and indoor display panel for the smart mobile phone. The adhesive sheet 10 is used for bonding elements contained in the laminated structure to each other, for example, in a process of manufacturing a rollable display panel.

The adhesive sheet 10 has a peel strength F1 of 5N/20mm or more in a low-speed peel test (first low-speed peel test) of: the adhesive sheet 10 was attached to a glass plate and thereafter the resultant was subjected to heat and pressure treatment at 50℃under 0.5MPa for 15 minutes, and then the adhesive sheet 10 was peeled from the glass plate at 25℃under a peeling angle of 180℃and a drawing speed of 30 mm/min. The peel strength F1 at 25℃is preferably 5.5N/20mm or more, more preferably 6N/20mm or more, and still more preferably 6.5N/20mm or more. The peel strength F1 is, for example, 30N/20mm or less. Examples of the method for adjusting the peel strength F1 include selection of the type of the base polymer in the adhesive sheet 10, adjustment of the molecular weight, and adjustment of the blending amount. The choice of the type of base polymer includes the adjustment of the composition of the monomers forming the base polymer. The method of adjusting the peel strength F1 may include selection of the type of component other than the base polymer in the adhesive sheet 10 and adjustment of the blending amount of the component. As the component, a crosslinking agent, a silane coupling agent, and an oligomer can be cited. The peel strength adjustment method described above is also applicable to peel strengths F2 to F5 described later.

In the following low-speed pull test (first low-speed pull test), the adhesive sheet 10 has a pull adhesive strength B1 of 0.9N/mm ² or more: the first glass plate and the second glass plate were joined in the thickness direction by the adhesive sheet 10 and thereafter subjected to heat and pressure treatment at 50 ℃, 0.5MPa and 15 minutes, and then the first glass plate and the second glass plate were drawn at 25 ℃ and a drawing speed of 5 mm/minute to the opposite sides in the thickness direction from each other. The tensile bond strength B1 at 25℃is preferably 1.2N/mm ² or more, more preferably 1.5N/mm ² or more, still more preferably 1.8N/mm ² or more, particularly preferably 2N/mm ² or more. The tensile bond strength B1 is, for example, 15N/mm ² or less. Examples of the method for adjusting the tensile adhesive strength B1 include: the selection of the kind of the base polymer, the adjustment of the molecular weight, and the adjustment of the blending amount in the adhesive sheet 10. The choice of the type of base polymer includes the adjustment of the composition of the monomers forming the base polymer. As a method for adjusting the tensile adhesive strength B1, selection of the types of components other than the base polymer in the adhesive sheet 10 and adjustment of the blending amount of the components can be cited. As the component, a crosslinking agent, a silane coupling agent, and an oligomer can be cited. The above-described method of adjusting the pulling-on adhesive strength is similar to the pulling-on adhesive strengths B2 and B3 described later.

As described above, the peel strength F1 of the adhesive sheet 10 in the first low-speed peel test is 5N/20mm or more, preferably 5.5N/20mm or more, more preferably 6N/20mm or more, further preferably 6.5N/20mm or more, and the pull adhesive strength B1 in the first low-speed pull test is 0.9N/mm ² or more, preferably 1.2N/mm ² or more, more preferably 1.5N/mm ² or more, further preferably 1.8N/mm ² or more, and particularly preferably 2N/mm ² or more. For the adhesive sheet, a combination of the peel strength measured in the 180 ° peel test and the pull adhesive strength measured in the pull test in the thickness direction of the adhesive sheet can be used as an index concerning the adhesive force (adhesive function) of the adhesive sheet in all directions. On the other hand, an adhesive sheet (an adherend is wound) for a rollable display application is required to have a high adhesive function in all directions.

When the adherend is continuously subjected to stress from the adherend in a state where the adherend is wound with the adhesive sheet 10 attached thereto, the adhesive sheet 10 having both strong adhesive forces measured in the low speed test is suitable for ensuring good adhesion to the adherend and suppressing peeling from the adherend. Thus, the adhesive sheet 10 is suitable for rollable display applications.

The peel strength F1 (N/20 mm) and the pull adhesive strength B1 (N/mm ²) of the adhesive sheet 10 preferably satisfy F1.gtoreq. -1/3 XB1+7. Such a configuration is preferable for both the peel strength F1 and the pull-off adhesive strength B1, and is preferable for obtaining good results in terms of adhesion of the adhesive sheet 10 to an adherend, for example, in the case of performing a winding holding test and a bending holding test described later under an ambient temperature environment.

The peel strength F2 of the adhesive sheet 10 in the second low-speed peel test is preferably 4N/20mm or more, more preferably 4.2N/20mm or more, further preferably 4.5N/20mm or more, and the pull adhesive strength B2 in the second low-speed pull test is preferably 0.9N/mm ² or more, more preferably 1N/mm ² or more, further preferably 1.1N/mm ² or more, particularly preferably 1.2N/mm ² or more. The peel strength F2 is, for example, 30N/20mm or less. The tensile bond strength B2 is, for example, 15N/mm ² or less. The second low-speed peel test was the following peel test: the adhesive sheet was attached to a glass plate and thereafter the resultant was subjected to heat and pressure treatment at 50℃under 0.5MPa for 15 minutes, and then the adhesive sheet was peeled from the glass plate at 50℃under a peeling angle of 180℃and a drawing speed of 30 mm/min. The second low-speed pull test is the following pull test: the first glass plate and the second glass plate were joined in the thickness direction by an adhesive sheet and thereafter subjected to heat and pressure treatment at 50 ℃, 0.5MPa and 15 minutes, and then the first glass plate and the second glass plate were drawn at 50 ℃ and a drawing speed of 5 mm/minute to the opposite sides in the thickness direction from each other.

When the adherend is continuously subjected to stress from the adherend in a state where the adherend is wound with the adhesive sheet 10 attached thereto, such an adhesive sheet 10 is preferable in order to ensure good adhesion to the adherend and to suppress peeling from the adherend at a temperature of 50 ℃ and the vicinity thereof.

The peel strength F2 (N/20 mm) and the pull adhesive strength B2 (N/mm ²) of the adhesive sheet 10 preferably satisfy F2.gtoreq. -1/3 XB2+5. Such a configuration is preferable for both the peel strength F2 and the pull-off adhesive strength B2, and is preferable for obtaining good results in terms of adhesion of the adhesive sheet 10 to an adherend in a winding-up holding test and a bending holding test described later under a high-temperature environment, for example.

The peel strength F3 of the adhesive sheet 10 in the third low-speed peel test is preferably 3N/20mm or more, more preferably 3.1N/20mm or more, further preferably 3.2N/20mm or more, and the pull adhesive strength B3 in the third low-speed pull test is preferably 0.9N/mm ² or more, more preferably 1N/mm ² or more, further preferably 1.1N/mm ² or more, particularly preferably 1.2N/mm ² or more. The peel strength F3 is, for example, 30N/20mm or less. The tensile bond strength B3 is, for example, 15N/mm ² or less. The third low-speed peel test was the following peel test: the adhesive sheet was attached to a glass plate and thereafter the resultant was subjected to heat and pressure treatment at 50℃under 0.5MPa for 15 minutes, and then the adhesive sheet was peeled from the glass plate at 80℃under a peeling angle of 180℃and a drawing speed of 30 mm/min. The third low-speed pull test is the following pull test: the first glass plate and the second glass plate were joined in the thickness direction by the adhesive sheet 10 and thereafter subjected to heat and pressure treatment at 50 ℃, 0.5MPa and 15 minutes, and then the first glass plate and the second glass plate were drawn at 80 ℃ and a drawing speed of 5 mm/minute to the opposite sides in the thickness direction from each other.

When the adherend is continuously subjected to stress from the adherend in a state where the adherend is wound with the adhesive sheet 10 attached thereto, such an adhesive sheet 10 is preferable in order to ensure good adhesion to the adherend and to suppress peeling from the adherend at a temperature range of 80 ℃ and the vicinity thereof.

The ratio (F4/F1) of the peel strength F4 to the peel strength F1 of the adhesive sheet 10 in the fourth low-speed peel test is preferably 0.48 or less, more preferably 0.46 or less, and still more preferably 0.44 or less. The ratio (F4/F1) is preferably 0.05 or more, more preferably 0.1 or more, and still more preferably 0.15 or more. The fourth low-speed peel test was the following peel test: the adhesive sheet was attached to a glass plate and thereafter the resultant was subjected to heat and pressure treatment at 50℃under 0.5MPa for 15 minutes, and then the adhesive sheet was peeled from the glass plate at 95℃under a peeling angle of 180℃and a drawing speed of 30 mm/min.

Such a configuration is preferable for both the peel strength F1 and the peel strength F4, and is preferable for obtaining good results in terms of adhesion of the adhesive sheet 10 to an adherend in a winding-up holding test and a bending holding test described later under a high-temperature environment, for example. While the ratio (F4/F1) satisfies the above range, the peel strength F4 is preferably 1N/20mm or more, more preferably 1.3N/20mm or more, further preferably 1.5N/20mm or more, and the peel strength F4 is preferably 5N/20mm or less, more preferably 4N/20mm or less, further preferably 3N/20mm or less.

The ratio (F5/F1) of the peel strength F5 to the peel strength F1 of the adhesive sheet 10 in the fifth low-speed peel test is preferably 0.45 or less, more preferably 0.42 or less, still more preferably 0.4 or less, and particularly preferably 0.38 or less. The ratio (F5/F1) is preferably 0.05 or more, more preferably 0.1 or more, and still more preferably 0.15 or more. The fifth low-speed peel test was the following peel test: the adhesive sheet was attached to a glass plate and thereafter the resultant was subjected to heat and pressure treatment at 50℃under 0.5MPa for 15 minutes, and then the adhesive sheet was peeled from the glass plate under conditions of 65℃and relative humidity of 90%, peeling angle of 180℃and drawing speed of 30 mm/min.

Such a configuration is preferable for both the peel strength F1 and the peel strength F5, and is preferable for obtaining good results in terms of adhesion of the adhesive sheet 10 to an adherend in a winding-up holding test and a bending holding test described later under a high-temperature environment, for example. While the ratio (F5/F1) satisfies the above range, the peel strength F5 is preferably 1N/20mm or more, more preferably 1.3N/20mm or more, still more preferably 1.5N/20mm or more, and further preferably 5N/20mm or less, more preferably 4N/20mm or less, still more preferably 3N/20mm or less.

The adhesive sheet 10 has a peel strength F6 of 10N/20mm or more in the following peel test (first normal speed peel test), which is the following peel test: the adhesive sheet 10 was attached to a glass plate and thereafter the resultant was subjected to heat and pressure treatment at 50℃under 0.5MPa for 15 minutes, and then the adhesive sheet 10 was peeled from the glass plate at 25℃under a peeling angle of 180℃and a drawing speed of 300 mm/min. The peel strength F6 is preferably 11N/20mm or more, more preferably 12N/20mm or more, and still more preferably 13N/20mm or more. When the adherend to which the adhesive sheet 10 is attached is wound under normal temperature conditions (dynamic deformation process), such a configuration is preferable in order to ensure good adhesion to the adherend in the adhesive sheet 10 and to suppress peeling from the adherend. The peel strength F6 is, for example, 30N/20mm or less.

The adhesive sheet 10 has a peel strength F7 of 8N/20mm or more in the following peel test (second normal speed peel test), which is the following peel test: the adhesive sheet 10 was attached to a glass plate and thereafter the resultant was subjected to heat and pressure treatment at 50℃under 0.5MPa for 15 minutes, and then the adhesive sheet 10 was peeled from the glass plate under conditions of 95℃at a peeling angle of 180℃and a drawing speed of 300 mm/min. The peel strength F7 is preferably 9N/20mm or more, more preferably 10N/20mm or more, and still more preferably 11N/20mm or more. Such a configuration is preferable for ensuring good adhesion to the adherend in the adhesive sheet 10 and suppressing peeling from the adherend when the adherend to which the adhesive sheet 10 is adhered is wound under a high temperature environment. The peel strength F7 is, for example, 30N/20mm or less.

In the following peel test (third conventional rate peel test), the adhesive sheet 10 has a peel strength F8 of 8N/20mm or more, which is the following peel test: the adhesive sheet 10 was attached to a glass plate and thereafter the resultant was subjected to heat and pressure treatment at 50℃under 0.5MPa for 15 minutes, and then the adhesive sheet 10 was peeled from the glass plate under conditions of 65℃and relative humidity of 90%, peeling angle of 180℃and drawing speed of 300 mm/min. The peel strength F8 is preferably 9N/20mm or more, more preferably 10N/20mm or more, and still more preferably 11N/20mm or more. Such a configuration is preferable for ensuring good adhesion to the adherend in the adhesive sheet 10 and suppressing peeling from the adherend when the adherend to which the adhesive sheet 10 is adhered is wound under a high humidity environment. The peel strength F8 is, for example, 30N/20mm or less.

The adhesive sheet 10 is a pressure-sensitive adhesive layer formed of an adhesive composition. The adhesive sheet 10 contains at least a base polymer.

The base polymer is an adhesive component that exhibits adhesiveness in the adhesive sheet. Examples of the base polymer include: acrylic polymers, polysiloxane polymers, polyester polymers, polyurethane polymers, polyamide polymers, polyvinyl ether polymers, vinyl acetate/vinyl chloride copolymers, modified polyolefin polymers, epoxy polymers, fluoropolymers, and rubber polymers. The base polymer may be used alone, or two or more kinds may be used in combination. From the viewpoint of ensuring good transparency and adhesion in the adhesive sheet, an acrylic polymer is preferably used as the base polymer.

The acrylic polymer is a copolymer containing a monomer component of an alkyl (meth) acrylate in a proportion of 50 mass% or more. "(meth) acrylic" refers to acrylic and/or methacrylic.

As the alkyl (meth) acrylate, an alkyl (meth) acrylate having an alkyl group with 1 to 20 carbon atoms is preferably used. The alkyl (meth) acrylate may have a linear alkyl group or a branched alkyl group, or may have a cyclic alkyl group such as an alicyclic alkyl group.

Examples of the alkyl (meth) acrylate having a linear alkyl group or a branched alkyl group include: methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, isobutyl (meth) acrylate, sec-butyl (meth) acrylate, tert-butyl (meth) acrylate, pentyl (meth) acrylate, isopentyl (meth) acrylate, neopentyl (meth) acrylate, hexyl (meth) acrylate, heptyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, octyl (meth) acrylate, isooctyl (meth) acrylate, nonyl (meth) acrylate, isononyl (meth) acrylate, decyl (meth) acrylate, isodecyl (meth) acrylate, undecyl (meth) acrylate, dodecyl (i.e., lauryl (meth) acrylate, isotridecyl (meth) acrylate, tetradecyl (meth) acrylate, isotetradecyl (meth) acrylate, pentadecyl (meth) acrylate, hexadecyl (meth) acrylate, heptadecyl (meth) acrylate, octadecyl (meth) acrylate, isooctadecyl (meth) acrylate and nonadecyl (meth) acrylate.

Examples of the alkyl (meth) acrylate having an alicyclic alkyl group include: cycloalkyl (meth) acrylates, (meth) acrylates having a bicyclic aliphatic hydrocarbon ring, and (meth) acrylates having an aliphatic hydrocarbon ring having three or more rings. Examples of the cycloalkyl (meth) acrylate include: cyclopentyl (meth) acrylate, cyclohexyl (meth) acrylate, cycloheptyl (meth) acrylate, and cyclooctyl (meth) acrylate. Examples of the (meth) acrylate having a bicyclic aliphatic hydrocarbon ring include isobornyl (meth) acrylate. Examples of the (meth) acrylate having an aliphatic hydrocarbon ring having three or more rings include: tetrahydrodicyclopentadiene (meth) acrylate, tetrahydrodicyclopentadiene oxyethyl (meth) acrylate, tetrahydrotricyclopentadienyl (meth) acrylate, 1-adamantyl (meth) acrylate, 2-methyl-2-adamantyl (meth) acrylate and 2-methyl-2-adamantyl (meth) acrylate.

As the alkyl (meth) acrylate, an alkyl acrylate having an alkyl group having 3 to 15 carbon atoms is preferably used, and more preferably at least one selected from the group consisting of n-butyl acrylate, 2-ethylhexyl acrylate and dodecyl acrylate can be used.

The proportion of the alkyl (meth) acrylate in the monomer component is preferably 50% by mass or more, more preferably 70% by mass or more, further preferably 90% by mass or more, particularly preferably 94% by mass or more, from the viewpoint of appropriately exhibiting basic characteristics such as adhesiveness in the adhesive sheet. The ratio is, for example, 99 mass% or less.

The monomer component may comprise a copolymerizable monomer capable of copolymerizing with the alkyl (meth) acrylate. Examples of the copolymerizable monomer include monomers having a polar group. Examples of the polar group-containing monomer include: hydroxyl group-containing monomers, carboxyl group-containing monomers, and monomers having a nitrogen atom-containing ring. The polar group-containing monomer contributes to introducing crosslinking points into the acrylic polymer and securing modification of the acrylic polymer such as cohesive force of the acrylic polymer.

Examples of the hydroxyl group-containing monomer include: 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, 6-hydroxyhexyl (meth) acrylate, 8-hydroxyoctyl (meth) acrylate, 10-hydroxydecyl (meth) acrylate, 12-hydroxylauryl (meth) acrylate and (4-hydroxymethylcyclohexyl) methyl (meth) acrylate. As the hydroxyl group-containing monomer, at least one selected from the group consisting of 4-hydroxybutyl acrylate and 2-hydroxyethyl acrylate is preferably used.

The proportion of the hydroxyl group-containing monomer in the monomer component is preferably 0.1 mass% or more, more preferably 0.5 mass% or more, and even more preferably 0.8 mass% or more, from the viewpoints of introducing a crosslinked structure into the acrylic polymer and securing the cohesive force of the adhesive sheet. From the viewpoint of adjusting the polarity of the acrylic polymer (regarding the compatibility of various additive components in the adhesive sheet with the acrylic polymer), this ratio is preferably 20 mass% or less, more preferably 10 mass% or less.

Examples of the carboxyl group-containing monomer include: acrylic acid, methacrylic acid, carboxyethyl acrylate, carboxypentyl acrylate, itaconic acid, maleic acid, fumaric acid, crotonic acid and isocrotonic acid.

The proportion of the carboxyl group-containing monomer in the monomer component is preferably 0.1 mass% or more, more preferably 0.5 mass% or more, and even more preferably 0.8 mass% or more, from the viewpoints of introducing a crosslinked structure into the acrylic polymer, ensuring cohesive force of the adhesive sheet, and ensuring adhesion of the adhesive sheet to an adherend. From the viewpoint of adjusting the glass transition temperature of the acrylic polymer and avoiding the risk of corrosion of the adherend by the acid, the ratio is preferably 30 mass% or less, more preferably 20 mass% or less.

In order to prevent corrosion of metal elements such as electrodes in a rollable display by acid components, the adhesive sheet 10 preferably has a small acid content. In the case where the adhesive sheet 10 is used for the adhesion of a polarizing plate, the adhesive sheet 10 preferably contains a small amount of acid in order to suppress the polyalkylene of the polyvinyl alcohol-based polarizer due to the acid component. In such an acid-free adhesive sheet 10, the content of the organic acid monomer (e.g., (meth) acrylic acid and carboxyl group-containing monomer) is preferably 100ppm or less, more preferably 70ppm or less, and still more preferably 50ppm or less. The organic acid monomer content of the adhesive sheet can be determined as follows: the acid monomer extracted into water by immersing the adhesive sheet in pure water and heating at 100 ℃ for 45 minutes was quantified by ion chromatography.

From the standpoint of acid-free, it is preferable that the base polymer in the adhesive sheet 10 contains substantially no organic acid monomer as a monomer component. The proportion of the organic acid monomer in the monomer component is preferably 0.5 mass% or less, more preferably 0.1 mass% or less, still more preferably 0.05 mass% or less, and still more preferably 0 mass% or less, from the viewpoint of acid-free.

Examples of the monomer having a nitrogen atom-containing ring include: n-vinyl-2-pyrrolidone, N-methyl vinyl pyrrolidone, N-vinyl pyridine, N-vinyl piperidone, N-vinyl pyrimidine, N-vinyl piperazine, N-vinyl pyrazine, N-vinyl pyrrole, N-vinyl imidazole, N-vinylOxazole, N- (meth) acryloyl-2-pyrrolidone, N- (meth) acryloylpiperidine, N- (meth) acryloylpyrrolidine, N-vinylmorpholine, N-vinyl-3-morpholone, N-vinyl-2-caprolactam, N-vinyl-1, 3-/>Oxazin-2-one, N-vinyl-3, 5-morpholindione, N-vinyl pyrazole, N-vinyl iso/>Oxazole, N-vinylthiazole and N-vinylisothiazole. As the monomer having a nitrogen atom-containing ring, N-vinyl-2-pyrrolidone is preferably used.

The proportion of the monomer having a nitrogen atom-containing ring in the monomer component is preferably 0.1 mass% or more, more preferably 0.3 mass% or more, and even more preferably 0.55 mass% or more, from the viewpoint of securing the cohesive force of the adhesive sheet and securing the adhesive force of the adhesive sheet to the adherend. From the viewpoints of adjusting the glass transition temperature of the acrylic polymer and adjusting the polarity of the acrylic polymer (regarding the compatibility of various additive components in the adhesive sheet with the acrylic polymer), the ratio is preferably 30 mass% or less, more preferably 20 mass% or less.

The monomer component may comprise other copolymerizable monomers. Examples of other copolymerizable monomers include: anhydride monomer, sulfonic acid group-containing monomer, phosphoric acid group-containing monomer, epoxy group-containing monomer, cyano group-containing monomer, alkoxy group-containing monomer, and aromatic vinyl compound. These other copolymerizable monomers may be used alone or in combination of two or more.

The base polymer preferably has a crosslinked structure. As a method for introducing the crosslinked structure into the base polymer, there can be mentioned: a method (first method) of compounding a base polymer having a functional group capable of reacting with a crosslinking agent and the crosslinking agent into an adhesive composition, and allowing the base polymer and the crosslinking agent to react in an adhesive sheet; and a method (second method) of forming a base polymer having a branched structure (crosslinked structure) incorporated in a polymer chain by polymerization of a monomer component forming the base polymer, including a polyfunctional monomer. These methods may be used in combination.

Examples of the crosslinking agent used in the first method include compounds that react with functional groups (e.g., hydroxyl groups and carboxyl groups) contained in the base polymer. Examples of such a crosslinking agent include: isocyanate crosslinking agent, peroxide crosslinking agent, epoxy crosslinking agent,Oxazoline crosslinkers, aziridine crosslinkers, carbodiimide crosslinkers, and metal chelate crosslinkers. The crosslinking agent may be used alone, or two or more thereof may be used in combination. As the crosslinking agent, an isocyanate crosslinking agent, a peroxide crosslinking agent and an epoxy crosslinking agent are preferably used because of high reactivity with hydroxyl groups and carboxyl groups in the base polymer and easy introduction of a crosslinked structure.

Examples of the isocyanate crosslinking agent include: toluene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, xylylene diisocyanate, hydrogenated xylylene diisocyanate, diphenylmethane diisocyanate, hydrogenated diphenylmethane diisocyanate, tetramethylxylylene diisocyanate, naphthalene diisocyanate, triphenylmethane triisocyanate and polymethylene polyphenyl isocyanates. In addition, as the isocyanate crosslinking agent, derivatives of these isocyanates can be mentioned. Examples of the isocyanate derivative include isocyanurate modified products and polyol modified products. Examples of the commercial products of the isocyanate crosslinking agent include: coronate L (trimethylolpropane adduct of toluene diisocyanate, manufactured by Tosoh corporation), coronate HL (trimethylolpropane adduct of hexamethylene diisocyanate, manufactured by Tosoh corporation), coronate HX (isocyanurate form of hexamethylene diisocyanate, manufactured by Tosoh corporation), TAKENATE D N (trimethylolpropane adduct of xylylene diisocyanate, manufactured by Sanjing chemical Co., ltd.), and Takenate 600 (1, 3-bis (isocyanatomethyl) cyclohexane, manufactured by Sanjing chemical Co., ltd.).

As peroxide crosslinking agents, there may be mentioned: dibenzoyl peroxide, bis (2-ethylhexyl) peroxydicarbonate, bis (4-tert-butylcyclohexyl) peroxydicarbonate, di-sec-butyl peroxydicarbonate, tert-butyl peroxyneodecanoate and tert-butyl peroxypivalate.

As the epoxy crosslinking agent, there may be mentioned: bisphenol A, epichlorohydrin type epoxy resin, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerol triglycidyl ether, 1, 6-hexanediol glycidyl ether, trimethylolpropane triglycidyl ether, diglycidyl aniline, diamine glycidyl amine, N, N, N ', N ' -tetraglycidyl m-xylylenediamine and 1, 3-bis (N, N ' -diglycidyl aminomethyl) cyclohexane.

From the viewpoint of ensuring the flexibility of the adhesive sheet 10, isocyanate crosslinking agents (particularly difunctional isocyanate crosslinking agents) and peroxide crosslinking agents are preferable. From the viewpoint of ensuring the durability of the adhesive sheet 10, an isocyanate crosslinking agent (particularly, a trifunctional isocyanate crosslinking agent) is preferable. In contrast to the base polymer, which forms softer two-dimensional crosslinks, the difunctional isocyanate crosslinker and the peroxide crosslinker form stronger three-dimensional crosslinks. From the viewpoint of achieving both durability and flexibility of the adhesive sheet 10, it is preferable to use a trifunctional isocyanate crosslinking agent in combination with a peroxide crosslinking agent and/or a difunctional isocyanate crosslinking agent.

From the viewpoint of ensuring the cohesive force of the adhesive sheet 10, the amount of the crosslinking agent to be blended is, for example, 0.01 parts by mass or more, preferably 0.05 parts by mass or more, and more preferably 0.07 parts by mass or more, relative to 100 parts by mass of the base polymer. From the viewpoint of ensuring good adhesion in the adhesive sheet 10, the amount of the crosslinking agent to be blended is, for example, 10 parts by mass or less, preferably 5 parts by mass or less, and more preferably 3 parts by mass or less, relative to 100 parts by mass of the base polymer.

In the above-described second method, the monomer component (including the polyfunctional monomer for introducing a crosslinked structure and other monomers) may be polymerized at one time or may be polymerized in multiple steps. In the multi-step polymerization method, first, a monofunctional monomer used for forming a base polymer is polymerized (prepolymerized), thereby producing a prepolymer composition containing a part of a polymer (a mixture of a polymer having a low degree of polymerization and an unreacted monomer). Next, a polyfunctional monomer is added to the prepolymer composition, and then a part of the polymer is polymerized with the polyfunctional monomer (main polymerization).

Examples of the polyfunctional monomer include polyfunctional (meth) acrylates having two or more ethylenically unsaturated double bonds in one molecule. As the polyfunctional monomer, a polyfunctional acrylate is preferable from the viewpoint that a crosslinked structure can be introduced by active energy ray polymerization (photopolymerization).

As the polyfunctional (meth) acrylate, there may be mentioned: difunctional (meth) acrylates, trifunctional (meth) acrylates and multifunctional (meth) acrylates of more than tetrafunctional.

Examples of the difunctional (meth) acrylate include: ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, tetraethylene glycol di (meth) acrylate, 1, 6-hexanediol di (meth) acrylate, 1, 9-nonanediol di (meth) acrylate, glycerol di (meth) acrylate, neopentyl glycol di (meth) acrylate, stearic acid modified pentaerythritol di (meth) acrylate, dihydro-dicyclopentadiene acrylate, di (meth) acryl isocyanurate, and alkylene oxide modified bisphenol di (meth) acrylate.

Examples of the trifunctional (meth) acrylate include: trimethylolpropane tri (meth) acrylate, pentaerythritol tri (meth) acrylate, and tris (acryloxyethyl) isocyanurate.

Examples of the polyfunctional (meth) acrylate having four or more functions include: di (trimethylolpropane) tetra (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol monohydroxy penta (meth) acrylate, alkyl modified dipentaerythritol pentaacrylate, and dipentaerythritol hexa (meth) acrylate.

The molecular weight of the polyfunctional monomer is preferably 1500 or less, more preferably 1000 or less. The functional group equivalent (g/eq) of the polyfunctional monomer is preferably 50 or more, more preferably 70 or more, and still more preferably 80 or more. The functional group equivalent is preferably 500 or less, more preferably 300 or less, and further preferably 200 or less. These configurations are preferable from the viewpoint of appropriately adjusting the viscoelasticity (e.g., storage modulus and dielectric loss tangent) by incorporating a crosslinked structure in the base polymer.

The acrylic polymer may be formed by polymerizing the above monomer components. Examples of the polymerization method include: solution polymerization, active energy ray polymerization (e.g., UV polymerization), bulk polymerization, and emulsion polymerization. From the viewpoints of transparency, water resistance, and cost of the adhesive sheet 10, solution polymerization and UV polymerization are preferable. As the solvent for the solution polymerization, for example, ethyl acetate and toluene can be used. As the initiator for polymerization, for example, a thermal polymerization initiator and a photopolymerization initiator can be used. The amount of the polymerization initiator used is, for example, 0.05 parts by mass or more and, for example, 1 part by mass or less based on 100 parts by mass of the monomer component.

Examples of the thermal polymerization initiator include: azo polymerization initiator and peroxide polymerization initiator. Examples of the azo polymerization initiator include: 2,2' -azobisisobutyronitrile, 2' -azobis (2-methylbutyronitrile), dimethyl 2,2' -azobis (2-methylpropionate), 4' -azobis (4-cyanovaleric acid), azobisisovaleronitrile, 2' -azobis (2-amidinopropane) dihydrochloride, 2' -azobis [2- (5-methyl-2-imidazolin-2-yl) propane ] dihydrochloride, 2' -azobis (2-methylpropionamidine) disulfate and 2,2' -azobis (N, N ' -dimethylene isobutyl amidine) dihydrochloride. Examples of the peroxide polymerization initiator include: dibenzoyl peroxide, t-butylmaleic anhydride and lauroyl peroxide.

Examples of the photopolymerization initiator include: benzoin ether photopolymerization initiator, acetophenone photopolymerization initiator, alpha-ketol photopolymerization initiator, aromatic sulfonyl chloride photopolymerization initiator, photoactive oxime photopolymerization initiator, benzoin photopolymerization initiator, benzil photopolymerization initiator, benzophenone photopolymerization initiator, ketal photopolymerization initiator, thioxanthone photopolymerization initiator, and acylphosphine oxide photopolymerization initiator.

In the polymerization, a chain transfer agent and/or a polymerization inhibitor (polymerization retarder) may be used for the purpose of molecular weight adjustment or the like. As the chain transfer agent, there may be mentioned: alpha-thioglycerol, dodecyl mercaptan, glycidyl mercaptan, thioglycollic acid, 2-mercaptoethanol, thioglycollic acid, 2-ethylhexyl thioglycolate, 2, 3-dimercapto-1-propanol, and alpha-methylstyrene dimer.

The molecular weight of the base polymer can be adjusted by adjusting the kind and/or amount of the polymerization initiator. For example, in radical polymerization, the higher the amount of the polymerization initiator, the higher the radical concentration of the reaction system, and therefore the density of the reaction initiation point is high, and the molecular weight of the base polymer to be formed tends to be small. On the other hand, the smaller the amount of the polymerization initiator, the lower the density of the reaction initiation point, and therefore the more easily the polymer chain is elongated, the larger the molecular weight of the base polymer to be formed tends to be.

The weight average molecular weight of the base polymer is preferably 10 ten thousand or more, more preferably 30 ten thousand or more, and even more preferably 50 ten thousand or more, from the viewpoint of securing the cohesive force in the adhesive sheet 10. The weight average molecular weight is preferably 500 ten thousand or less, more preferably 300 ten thousand or less, and still more preferably 200 ten thousand or less. The weight average molecular weight of the base polymer may be determined by Gel Permeation Chromatography (GPC) and calculated by polystyrene conversion.

The glass transition temperature (Tg) of the base polymer is preferably 0℃or lower, more preferably-10℃or lower, and further preferably-20℃or lower. The glass transition temperature is, for example, at least-80 ℃.

As for the glass transition temperature (Tg) of the base polymer, a glass transition temperature (theoretical value) obtained based on the following Fox formula can be used. The Fox equation is a relation between the glass transition temperature Tg of a polymer and the glass transition temperature Tgi of a homopolymer of monomers constituting the polymer. In the following Fox formula, tg represents the glass transition temperature (. Degree. C.) of the polymer, wi represents the weight fraction of the monomer i constituting the polymer, tgi represents the glass transition temperature (. Degree. C.) of the homopolymer formed from the monomer i. As regards the glass transition temperature of the homopolymer, literature values can be used. Examples include: glass transition temperatures of various homopolymers in Polymer handbook (fourth edition, john Wiley & Sons, inc., 1999) and synthetic resin entrance to novel Polymer library 7 coating (North Korea, polymer journal, 1995). On the other hand, the glass transition temperature of a homopolymer of a monomer can be determined by a method specifically described in Japanese patent application laid-open No. 2007-51271.

Fox equation 1/(273+tg) =Σ [ Wi/(273+tgi) ]

The adhesive composition may contain one or two or more oligomers in addition to the base polymer. In the case of using an acrylic polymer as a base polymer, an acrylic oligomer is preferably used as the oligomer. The acrylic oligomer is a copolymer containing a monomer component of an alkyl (meth) acrylate in an amount of 50 mass% or more, and has a weight average molecular weight of, for example, 1000 to 30000.

The glass transition temperature of the acrylic oligomer is preferably 60℃or higher, more preferably 80℃or higher, still more preferably 100℃or higher, particularly preferably 110℃or higher. The glass transition temperature of the acrylic oligomer is, for example, 200℃or less, preferably 180℃or less, and more preferably 160℃or less. By using the low Tg acrylic polymer (base polymer) and the high Tg acrylic oligomer together, which introduce a crosslinked structure, the adhesive force of the adhesive sheet 10, particularly the adhesive force at high temperature, can be improved. The glass transition temperature of the acrylic oligomer is calculated according to the Fox equation described above.

The acrylic oligomer having a glass transition temperature of 60 ℃ or higher is preferably a polymer containing a monomer component of an alkyl (meth) acrylate having a chain alkyl group (a chain alkyl (meth) acrylate) and an alkyl (meth) acrylate having an alicyclic alkyl group (an alicyclic alkyl (meth) acrylate). Specific examples of these alkyl (meth) acrylates include the alkyl (meth) acrylates described above as the monomer components of the acrylic polymer.

The chain alkyl (meth) acrylate is preferably methyl methacrylate because of its high glass transition temperature and excellent compatibility with the base polymer. As the alicyclic alkyl (meth) acrylate, tetrahydrodicyclopentadiene methacrylate, cyclohexyl acrylate and cyclohexyl methacrylate are preferable. That is, the acrylic oligomer is preferably a polymer containing one or more monomer components selected from the group consisting of tetrahydrodicyclopentadienyl acrylate, tetrahydrodicyclopentadienyl methacrylate, cyclohexyl acrylate and cyclohexyl methacrylate, and methyl methacrylate.

The proportion of the alicyclic alkyl (meth) acrylate in the monomer component of the acrylic oligomer is preferably 10% by mass or more, more preferably 20% by mass or more, and still more preferably 30% by mass or more. The proportion is preferably 90% by mass or less, more preferably 80% by mass or less, and still more preferably 70% by mass or less. The proportion of the chain alkyl (meth) acrylate in the monomer component of the acrylic oligomer is preferably 90 mass% or less, more preferably 80 mass% or less, and still more preferably 70 mass% or less. The proportion is preferably 10% by mass or more, more preferably 20% by mass or more, and still more preferably 30% by mass or more.

The weight average molecular weight of the acrylic oligomer is preferably 1000 or more, more preferably 1500 or more, and further preferably 2000 or more. The molecular weight is preferably 30000 or less, more preferably 10000 or less, and even more preferably 8000 or less. Such a molecular weight range of the acrylic oligomer is preferable for securing the adhesive force and adhesive holding force of the adhesive sheet 10.

The acrylic oligomer can be obtained by polymerizing the monomer components of the acrylic oligomer. Examples of the polymerization method include: solution polymerization, active energy ray polymerization (e.g., UV polymerization), bulk polymerization, and emulsion polymerization. The polymerization initiator may be used for polymerization of the acrylic oligomer, or a chain transfer agent may be used for the purpose of adjusting the molecular weight.

In order to sufficiently improve the adhesive strength of the adhesive sheet 10, the content of the acrylic oligomer in the adhesive sheet 10 is preferably 0.5 parts by mass or more, more preferably 0.8 parts by mass or more, and still more preferably 1 part by mass or more, relative to 100 parts by mass of the base polymer. On the other hand, from the viewpoint of ensuring transparency of the adhesive sheet 10, the content of the acrylic oligomer in the adhesive sheet 10 is preferably 5 parts by mass or less, more preferably 4 parts by mass or less, and still more preferably 3 parts by mass or less, relative to 100 parts by mass of the base polymer. In the pressure-sensitive adhesive sheet 10, when the content of the acrylic oligomer is too large, the haze tends to increase and the transparency tends to decrease due to a decrease in the compatibility of the acrylic oligomer.

The adhesive composition may contain a silane coupling agent. The content of the silane coupling agent in the adhesive composition is preferably 0.1 part by mass or more, more preferably 0.2 part by mass or more, with respect to 100 parts by mass of the base polymer. The content is preferably 5 parts by mass or less, more preferably 3 parts by mass or less.

The adhesive composition may contain other components as needed. Examples of the other components include: solvents, tackifiers, plasticizers, softeners, antioxidants, fillers, colorants, ultraviolet absorbers, antioxidants, surfactants, and antistatic agents. Examples of the solvent include: a polymerization solvent used when polymerizing the acrylic polymer as needed and a solvent added to the polymerization reaction solution after polymerization. As the solvent, for example, ethyl acetate and toluene can be used.

The adhesive sheet 10 can be produced, for example, by coating the adhesive composition described above on a release liner L1 (first release liner) to form a coating film, and then drying the coating film.

Examples of the release liner include a flexible plastic film. Examples of the plastic film include: polyester films such as polyethylene terephthalate films, polyethylene films and polypropylene films. The thickness of the release liner is, for example, 3 μm or more and, for example, 200 μm or less. The surface of the release liner is preferably subjected to a release treatment.

Examples of the method for applying the adhesive composition include: roll coating, roll licking coating, gravure coating, reverse coating, roll brushing, spray coating, dip roll coating, bar coating, knife coating, air knife coating, curtain coating, lip die coating, and die coating. The drying temperature of the coating film is, for example, 50 to 200 ℃. The drying time is, for example, 5 seconds to 20 minutes.

A release liner L2 (second release liner) may also be laminated on the adhesive sheet 10 on the first release liner L1. The second release liner is a flexible plastic film subjected to a surface release treatment, and the same release liners as those described above with respect to the first release liner can be used.

By the above operation, the adhesive sheet 10 having the adhesive surfaces 11 and 12 covered and protected by the release liners L1 and L2 can be manufactured. The release liners L1, L2 are peeled from the adhesive sheet 10 as necessary when the adhesive sheet 10 is used.

The thickness of the pressure-sensitive adhesive sheet 10 is preferably 10 μm or more, more preferably 15 μm or more, from the viewpoint of securing sufficient adhesion to an adherend. The thickness of the adhesive sheet 10 is preferably 300 μm or less, more preferably 200 μm or less, further preferably 100 μm or less, particularly preferably 50 μm or less, from the viewpoint of handleability of the adhesive sheet 10.

The haze of the pressure-sensitive adhesive sheet 10 is preferably 3% or less, more preferably 2% or less, and still more preferably 1% or less. The haze of the pressure-sensitive adhesive sheet 10 can be measured by a haze meter according to JIS K7136 (year 2000). Examples of the haze meter include "NDH2000" manufactured by Nippon electric color industry Co., ltd and "HM-150" manufactured by Country color technology research Co., ltd.

The total light transmittance of the pressure-sensitive adhesive sheet 10 is preferably 60% or more, more preferably 80% or more, and still more preferably 85% or more. The total light transmittance of the pressure-sensitive adhesive sheet 10 is, for example, 100% or less. The total light transmittance of the adhesive sheet 10 can be measured in accordance with JIS K7375 (2008).

Fig. 2A to 2C show an example of a method of using the pressure-sensitive adhesive sheet 10.

In this method, first, as shown in fig. 2A, the adhesive sheet 10 is attached to one surface of the first member 21 (adherend) in the thickness direction H. The first member 21 is, for example, one element of a laminated structure of a rollable display panel. Examples of the element include: a pixel panel, a polarizing plate (polarizing film), a touch panel, and a protective film (the same applies to the second member 22 described later). Through this step, the adhesive sheet 10 for bonding with other members is provided on the first member 21.

Next, as shown in fig. 2B, one surface side in the thickness direction H of the first member 21 and the other surface side in the thickness direction H of the second member 22 are joined by the adhesive sheet 10 on the first member 21. The second member 22 is, for example, another element in the laminated structure of the rollable display panel.

Next, as shown in fig. 2C, the adhesive sheet 10 between the first member 21 and the second member 22 is cured. By curing, a crosslinking reaction of the base polymer proceeds in the adhesive sheet 10, and the bonding force between the first member 21 and the second member 22 is improved. The curing temperature is, for example, 20℃to 160 ℃. The curing time is, for example, 1 minute to 21 days. When the curing is performed by autoclaving (heating and pressurizing), the temperature is, for example, 30 to 80℃and the pressure is, for example, 0.1 to 0.8MPa, and the treatment time is, for example, 15 minutes or longer.

The adhesive sheet 10 used in the above manner in the manufacturing process of the rollable display panel has a peel strength F1 of 5N/20mm or more in the first low-speed peel test and a pull adhesive strength B1 of 0.9N/mm ² or more in the first low-speed pull test, as described above. When the adherend is continuously subjected to stress from the adherend in a state where the adherend is wound with the adhesive sheet 10 attached thereto, such an adhesive sheet 10 having both strong adhesive forces measured in a low speed test is suitable for ensuring good adhesion to the adherend and suppressing peeling from the adherend. Thus, the adhesive sheet 10 is suitable for rollable display applications.

Examples

The present invention will be specifically described below with reference to examples. The invention is not limited to the examples. In addition, specific numerical values such as the blending amount (content), physical property value, parameter and the like described below may be substituted for the upper limit (numerical value defined as "below" or "less" or the lower limit (numerical value defined as "above" or "greater") of the blending amount (content), physical property value, parameter and the like corresponding to these described in the above-described "specific embodiment".

Example 1

< Preparation of adhesive composition >

In a flask, 0.05 part by mass of 2, 2-dimethoxy-1, 2-diphenyl-1-one (product name "Irgacure 651", manufactured by microb japan) as a first photopolymerization initiator and 0.05 part by mass of 1-hydroxycyclohexyl phenyl ketone (product name "Irgacure 184", manufactured by microb japan) as a second photopolymerization initiator were added to a monomer mixture containing 75 parts by mass of 2-ethylhexyl acrylate (2 EHA), 5 parts by mass of 4-hydroxybutyl acrylate (4 HBA), and 20 parts by mass of N-vinyl-2-pyrrolidone (NVP), and then the mixture was irradiated with ultraviolet rays under a nitrogen atmosphere, whereby a part of monomer components in the mixture was polymerized, thereby obtaining a first prepolymer composition (containing monomer components which were not subjected to polymerization reaction). Then, 100 parts by mass of the first prepolymer composition, 0.3 parts by mass of hexamethyleneglycol diacrylate (HDDA) as a crosslinking agent, and 0.3 parts by mass of a silane coupling agent (product name "KBM403", manufactured by the company of the surthe chemical industry, inc.) were mixed to obtain a first adhesive composition.

< Formation of adhesive layer >

A first release liner (product name "Diafoil MRF", 38 μm thick, manufactured by Mitsubishi chemical corporation) having a release treated surface on one side was coated with a first adhesive composition on the release treated surface, thereby forming a coating film. Next, a release treated surface of a second release liner (product name "Diafoil MRN", thickness 38 μm, manufactured by Mitsubishi chemical corporation) having a release treated surface on one side was bonded to the coating film on the first release liner. Subsequently, the coating film between the release liners was irradiated with ultraviolet light, and the coating film was photo-cured, thereby forming an adhesive layer (thickness: 50 μm). In ultraviolet irradiation, a metal halide lamp was used as a light source, the illuminance was set to 4mW/cm ², and the irradiation cumulative light amount was set to 1200mJ/cm ².

An optical adhesive sheet (thickness 50 μm) of example 1 with a double-sided release liner was produced by the above operation.

Example 2

< Preparation of adhesive composition >

In a flask, 0.05 part by mass of 2, 2-dimethoxy-1, 2-diphenyl-1-one (product name "Irgacure 651", manufactured by kikai) as a first photopolymerization initiator and 0.05 part by mass of 1-hydroxycyclohexyl phenyl ketone (product name "Irgacure 184", manufactured by kikai) as a second photopolymerization initiator were added to a monomer mixture containing 80 parts by mass of Butyl Acrylate (BA), 10 parts by mass of 4-hydroxybutyl acrylate (4 HBA), and 10 parts by mass of cyclohexyl acrylate, and then the mixture was irradiated with ultraviolet rays under a nitrogen atmosphere, whereby a second prepolymer composition having a polymerization ratio of 10% was obtained (containing monomer components which were not subjected to polymerization reaction). Then, 100 parts by mass of the second prepolymer composition, 0.01 parts by mass of dipentaerythritol hexaacrylate (DPHA) as a crosslinking agent, and 0.3 parts by mass of a silane coupling agent (product name "KBM403", manufactured by the company of the shiny chemical industry) were mixed, thereby obtaining a second adhesive composition.

< Formation of adhesive layer >

The first adhesive composition was coated on the release treated surface of a first release liner (product name "Diafoil MRF", thickness 38 μm, manufactured by mitsubishi chemical company) having a release treated surface on one side, thereby forming a coating film. Next, a release treated surface of a second release liner (product name "Diafoil MRN", thickness 38 μm, manufactured by Mitsubishi chemical corporation) having a release treated surface on one side was bonded to the coating film on the first release liner. Subsequently, the coating film between the release liners was irradiated with ultraviolet light, and the coating film was photo-cured, thereby forming an adhesive layer (thickness: 50 μm). In ultraviolet irradiation, a metal halide lamp was used as a light source, the illuminance was set to 4mW/cm ², and the irradiation cumulative light amount was set to 1200mJ/cm ².

An optical adhesive sheet (thickness 50 μm) of example 2 with a double-sided release liner was produced by the above operation.

Comparative example 1

An optical pressure-sensitive adhesive sheet with a double-sided release liner (50 μm) of comparative example 1 was produced in the same manner as in the optical pressure-sensitive adhesive sheet with a double-sided release liner of example 2 except that the amount of DPHA blended was changed from 0.01 parts by mass to 0.1 parts by mass in the preparation of the pressure-sensitive adhesive composition.

< Low speed Peel test >

The peel strength in the low-speed peel test was studied for each of the optical adhesive sheets of examples 1,2 and comparative example 1.

Specifically, first, a necessary number of measurement samples are prepared for each optical adhesive sheet. In the production of the test sample, first, the first release liner was peeled off from the optical adhesive sheet, and the exposed surface thus exposed was bonded to a polyethylene terephthalate (PET) film (product name "Lumirror S10", manufactured by eastern co., thickness 50 μm) having been subjected to plasma treatment, to obtain a laminate. Then, a test piece (width 20 mm. Times. Length 100 mm) was cut out from the laminate (PET film/optical adhesive sheet/second release liner). Then, the second release liner was peeled off from the optical adhesive sheet in the test piece, and the exposed surface thus exposed was bonded to a glass plate (product name "SLIDE GLASS S2004U8", manufactured by songarde glass industry corporation). Next, the glass plate with the adhesive sheet (test piece) was subjected to heating and pressurizing treatment at a temperature of 50℃and a pressure of 0.5MPa for 15 minutes. The test piece was thereby crimped onto the glass plate. The measurement sample was prepared by the above procedure.

Then, the measurement sample was allowed to stand at room temperature for 30 minutes, and then a low-speed peel test was performed to peel the test piece from the glass plate of the measurement sample, whereby the peel strength was measured (first test). In this measurement, a tensile tester (product name "Autograph AG-50NX plus)", manufactured by Shimadzu corporation, was used. In this measurement, the measurement temperature was set to 25 ℃, the relative humidity was set to 55%, the peeling angle of the test piece from the glass plate was set to 180 °, the drawing speed of the test piece was set to 30 mm/min, and the peeling length was set to 50mm. The average value of the measured peel strengths is shown in Table 1 as peel strength F1 (N/20 mm).

The low-speed peel test was performed under the same conditions as the first test except that the measurement temperature was changed to 50 ℃, thereby measuring the peel strength F2 at 50 ℃. The low-speed peel test was performed under the same conditions as the first test except that the measurement temperature was changed to 80 ℃, thereby measuring the peel strength F3 at 80 ℃. The low-speed peel test was performed under the same conditions as the first test except that the measurement temperature was changed to 95 ℃, thereby measuring the peel strength F4 at 95 ℃. The low-speed peel test was performed under the same conditions as the first test except that the measurement temperature was changed to 65 ℃ and the relative humidity was set to 90%, thereby measuring the peel strength F5 at 65 ℃ and the relative humidity of 90%. Table 1 also shows the peel strengths F2 to F5, the ratio of the peel strength F4 to the peel strength F1 (F4/F1), and the ratio of the peel strength F5 to the peel strength F1 (F5/F1).

< Low speed traction test >)

The optical adhesive sheets of examples 1,2 and comparative example 1 were each investigated for the tensile adhesive strength in the low-speed tensile test. Specifically, the following is described.

First, a measurement sample was prepared for each optical adhesive sheet. In the production of a measurement sample, first, two glass plates supported by a metal block are prepared. The metal block supporting glass plate was prepared as follows: a glass plate (3 cm. Times.3 cm. Times.0.5 cm) was attached to one surface of a metal block (3 cm. Times.3 cm cube block made of SUS 304) by an adhesive. Then, the first release liner of the optical adhesive sheet (1 cm×1 cm) cut from the optical adhesive sheet was peeled off, and the exposed surface thus exposed was bonded to the glass exposed surface of one metal block supporting glass plate (first glass plate). Then, the second release liner is peeled off from the optical adhesive sheet on the glass plate, the exposed surface thus exposed is bonded to the glass exposed surface of the other metal block supporting glass plate (second glass plate), and the glass plates are bonded to each other (the first glass plate and the second glass plate are bonded in the thickness direction by the optical adhesive sheet). Next, the optical adhesive sheet test piece was pressure-bonded to two glass plates by heating and pressurizing at a temperature of 50℃and a pressure of 0.5MPa for 15 minutes. By the above procedure, a measurement sample (metal block/glass plate/optical adhesive sheet/glass plate/metal block) was prepared.

Next, a test (low-speed pulling test) was performed in which two metal supporting glass plates in the measurement sample were pulled to opposite sides in the thickness direction, and the force required to pull apart the glass plates was measured (second test). In this measurement, a tensile tester (product name "Autograph AG-50NX plus)", manufactured by Shimadzu corporation, was used. In this measurement, the measurement temperature was set at 25℃and the relative humidity was set at 55%, and the pulling speed was set at 5 mm/min. The maximum value of the measured force is shown in Table 1 as the pulling-on adhesive strength B1 (N/mm ²).

The low-speed pulling test was performed under the same conditions as the second test except that the measurement temperature was changed to 50 ℃, thereby measuring the pulling-on adhesive strength B2 at 50 ℃. The low-speed pulling test was performed under the same conditions as the second test except that the measurement temperature was changed to 80 ℃, and the pulling-on adhesive strength B3 at 80 ℃ was measured. Their values are also shown in table 1.

The results of the measurement of the peel strength and the pull-out adhesive strength of each of the optical adhesive sheets of examples 1 and 2 and comparative example 1 are shown in the graph of fig. 3. In the graph of FIG. 3, the horizontal axis represents the tensile adhesive strength (N/mm ²) in the low-speed tensile test, and the vertical axis represents the peel strength (N/20 mm) in the low-speed peel test. In fig. 3, a curve E1 represents the measurement result in example 1, a curve E2 represents the measurement result in example 2, and a curve C1 represents the measurement result in comparative example 1. In addition, a broken line R1 represents a line of the pull adhesive strength b=0.9N/mm ². The chain line R2 represents a line with peel strength f= -1/3 x pull adhesive strength b+7. The two-dot chain line R3 represents a line having peel strength f= -1/3×pull adhesive strength b+5. The optical adhesive sheets of examples 1,2 satisfied F.gtoreq. -1/3 XB+7 in peel strength F (N/20 mm) and traction adhesive strength B (N/mm ²) at 25℃and F.gtoreq. -1/3 XB+5 in peel strength F (N/20 mm) and traction adhesive strength B (N/mm ²) at 50 ℃. The optical adhesive sheets of examples 1 and 2 showed good results in a winding holding test described later and good results in a bending holding test described later.

< Winding hold test >

The optical adhesive sheets of examples 1 and 2 and comparative example 1 were subjected to a roll holding test as follows.

The first release liner was peeled from the optical adhesive sheet, and a first PET film (product name "Lumirror S10", thickness 100 μm, manufactured by ori corporation) having been subjected to plasma treatment was bonded to the exposed surface, thereby producing a first laminate. Then, a release liner was peeled off from the adhesive layer of the polarizing plate with an adhesive (PSA) layer (thickness: 66 μm, a releasable release liner was provided on the outer surface of the adhesive layer, and a releasable protective film was provided on the outer surface of the polarizing plate, manufactured by solar corporation), and a second PET film (product name "Lumirror S10", thickness: 188 μm, manufactured by eastern corporation) having a plasma-treated surface was bonded to the exposed surface, thereby producing a second laminate. Next, the second release liner was peeled off from the optical adhesive sheet of the first laminate, the protective film was peeled off from the polarizing plate in the second laminate, the exposed surfaces thus exposed were bonded to each other, and the third laminate (first PET film/optical adhesive sheet/PSA/second PET film on polarizing plate/polarizing plate) was produced by pressure-heating treatment at 50 ℃ under 0.5MPa and 15 minutes. Then, a test piece (width 25 mm. Times. Length 150 mm) was cut out from the third laminate. The test piece has a first end portion at one end in the longitudinal direction and a second end portion at the other end.

Next, the test piece was wound around a cylindrical metal rod (manufactured by SUS 304) having a cross-sectional diameter of 30mm so that the longitudinal direction of the test piece was along the circumferential direction of the metal rod as follows. First, a first PET film side of a first end portion of the test piece was attached to a metal rod via a double-sided tape. Next, the test piece was wound around the metal rod while being pulled in the longitudinal direction so that the first PET film side of the test piece was disposed inside the winding. Specifically, the test piece was wound around the metal rod so that there was no gap between the metal rod and the test piece and no gap between the test pieces in the radial direction of the metal rod. Next, the second end portion was fixed to the test piece wound around the metal rod by an adhesive tape.

Next, the metal bar with test piece produced by the above operation was allowed to stand at 60 ℃ and an environment of 95% relative humidity for 250 hours (winding hold test). In addition, regarding the adhesiveness of the optical adhesive sheet to the adherend in such a winding holding test, the occurrence of any failure such as air bubbles and peeling in the adhesive layer (optical adhesive sheet) and breakage of the polarizing plate was evaluated as "good", and the occurrence of any failure was evaluated as "bad". The results are shown in Table 1.

< Bending hold test >

The optical adhesive sheets of examples 1, 2 and comparative example 1 were subjected to a bending retention test as follows.

First, test pieces (width 25 mm. Times. Length 150mm, laminated constitution: first PET film/optical adhesive sheet/polarizing plate/PSA/second PET film on polarizing plate) similar to those described above for the winding hold test were produced. Then, the test piece was bent and deformed from a flat shape to a U-shape, and the deformed test piece was held by a predetermined holding tool. Specifically, the center portion in the longitudinal direction of the test piece was bent so that the first PET film side of the first end portion of the test piece faced the first PET film side of the second end portion (the distance between the facing end portions was about 20 mm) with respect to the test piece in the deformed state. Then, the test piece in the deformed state was allowed to stand at 60℃under an environment of 95% relative humidity for 250 hours (bending hold test). In addition, regarding the adhesiveness of the optical adhesive sheet to the adherend in such a bending holding test, the occurrence of defects such as bubbles and peeling in the adhesive layer (optical adhesive sheet) and breakage of the polarizing plate was evaluated as "good", and the occurrence of any defect was evaluated as "bad". The results are shown in Table 1.

TABLE 1

Industrial applicability

The optical adhesive sheet of the present invention is used for bonding elements contained in a laminated structure of a rollable display panel to each other.

Description of the reference numerals

10. Adhesive sheet (optical adhesive sheet)

11. 12 Adhesive surface

H thickness direction

L1, L2 release liner

21. First component

22. Second component

Claims

1. An optical adhesive sheet, wherein,

In the low-speed peel test described below, the optical adhesive sheet has a peel strength F1 of 5N/20mm or more,

The low-speed peel test is as follows: attaching the optical adhesive sheet to a glass plate and thereafter subjecting the resultant to heat and pressure treatment at 50℃under 0.5MPa for 15 minutes, and then peeling the optical adhesive sheet from the glass plate at 25℃under a peeling angle of 180℃and a drawing speed of 30 mm/min,

In the low-speed pulling test described below, the optical adhesive sheet has a pulling-on adhesive strength B1 of 0.9N/mm ² or more,

The low-speed traction test is as follows: the first glass plate and the second glass plate were joined in the thickness direction by the optical adhesive sheet and thereafter subjected to the aforementioned heat-pressing treatment, and then the first glass plate and the second glass plate were drawn on the opposite sides to each other in the thickness direction under the conditions of 25 ℃ and a drawing speed of 5 mm/min.

2. The optical adhesive sheet according to claim 1, wherein the peel strength F1 (N/20 mm) and the pull adhesive strength B1 (N/mm ²) satisfy F1.gtoreq.1/3 XB1+7.

3. The optical adhesive sheet according to claim 1, wherein,

In the low-speed peel test described below, the optical adhesive sheet has a peel strength F2 of 4N/20mm or more,

The low-speed peel test is as follows: attaching the optical adhesive sheet to a glass plate and thereafter subjecting the resultant to the aforementioned heat and pressure treatment, and then peeling the optical adhesive sheet from the glass plate at 50℃under conditions of a peeling angle of 180℃and a drawing speed of 30 mm/min,

In the low-speed pulling test described below, the optical adhesive sheet has a pulling-on adhesive strength B2 of 0.9N/mm ² or more,

The low-speed traction test is as follows: the first glass plate and the second glass plate were joined in the thickness direction by the optical adhesive sheet and thereafter the resultant was subjected to the aforementioned heat and pressure treatment, and then the first glass plate and the second glass plate were drawn on the opposite sides to each other in the thickness direction under the conditions of 50 ℃ and a drawing speed of 5 mm/min.

4. An optical adhesive sheet according to claim 3, wherein the peel strength F2 (N/20 mm) and the pull adhesive strength B2 (N/mm ²) satisfy F2.gtoreq.1/3 XB2+5.

5. The optical adhesive sheet according to claim 1, wherein,

In the low-speed peel test described below, the optical adhesive sheet has a peel strength F3 of 3N/20mm or more,

The low-speed peel test is as follows: attaching the optical adhesive sheet to a glass plate and thereafter subjecting the resultant to the aforementioned heat and pressure treatment, and then peeling the optical adhesive sheet from the glass plate at 80℃under conditions of a peeling angle of 180℃and a drawing speed of 30 mm/min,

In the low-speed pulling test described below, the optical adhesive sheet has a pulling-on adhesive strength B3 of 0.9N/mm ² or more,

The low-speed traction test is as follows: the first glass plate and the second glass plate were joined in the thickness direction by the optical adhesive sheet and thereafter subjected to the aforementioned heat and pressure treatment, and then the first glass plate and the second glass plate were drawn on the opposite sides to each other in the thickness direction under conditions of 80 ℃ and a drawing speed of 5 mm/min.

6. The optical adhesive sheet according to claim 1, wherein the ratio of the peel strength F4 to the peel strength F1 in the low-speed peel test described below is 0.48 or less,

The low-speed peel test is as follows: the optical adhesive sheet was bonded to a glass plate and thereafter the resultant was subjected to the aforementioned heat and pressure treatment, and then the optical adhesive sheet was peeled from the glass plate under conditions of 95℃and a peeling angle of 180℃and a drawing speed of 30 mm/min.

7. The optical adhesive sheet according to claim 1, wherein the ratio of the peel strength F5 to the peel strength F1 in the low-speed peel test described below is 0.45 or less,

The low-speed peel test is as follows: the optical adhesive sheet was attached to a glass plate and thereafter the resultant was subjected to the aforementioned heat and pressure treatment, and then the optical adhesive sheet was peeled from the glass plate under conditions of 65℃and a relative humidity of 90%, a peeling angle of 180℃and a drawing speed of 30 mm/min.